A lithium secondary battery is known to include a large energy capacity and is thus utilized in various fields. Nevertheless, lithium is a scarce resource and is also expensive.
In addition, a magnesium secondary battery has been recently developed as an energy storage device that utilizes an oxidation-reduction reaction of magnesium. Magnesium is rich as a resource and is inexpensive. Therefore, the magnesium secondary battery is more expected as a future energy storage device than the lithium secondary battery.
A selection of nonaqueous liquid electrolyte used for the magnesium secondary battery affects a battery capability. Thus, a research regarding the nonaqueous liquid electrolyte for the magnesium secondary battery has been proceeded. JP2009-21085A which will be hereinafter referred to as Reference 1 discloses a nonaqueous liquid electrolyte for a magnesium secondary battery where magnesium chloride serving as an electrolyte and alkyl aluminum (dimethylaluminum chloride) serving as an additive are dissolved in tetrahydrofuran serving as a solvent. JP2009-64730A which will be hereinafter referred to as Reference 2 discloses a nonaqueous liquid electrolyte for a magnesium secondary battery where magnesium metal, halogenated hydrocarbon, aluminum halide, and quaternary ammonium salt are dissolved in an ether organic solvent.
In the nonaqueous liquid electrolyte disclosed in Reference 1, alkyl aluminum is used as the additive. In the nonaqueous liquid electrolyte disclosed in Reference 2, alkylmagnesium is generated by the reaction of magnesium metal and halogenated hydrocarbon in the solvent. Alkyl aluminum and alkylmagnesium generate a combustible gas by reacting with water, which leads to difficulty in handling. In addition, in the nonaqueous liquid electrolyte disclosed in each Reference 1 or 2, an oxidation-reduction current of magnesium is relatively small. Thus, in a case where the nonaqueous liquid electrolyte disclosed in each Reference 1 or 2 is used as an electrolyte for the magnesium secondary battery, it may be difficult to obtain a large output (i.e., voltage).
A need thus exists for a nonaqueous liquid electrolyte which is not susceptible to the drawback mentioned above.